Superhard insert and an earth boring tool comprising same

ABSTRACT

A superhard insert for a rotary earth borer tool comprises a cutter end having a peripheral cutter edge, at least part of the peripheral cutter edge being defined by a plurality of edges of a plurality of alternate hard and superhard regions. The edges of the superhard regions are arranged spaced apart from each other and are separated by edges of hard regions. The hardness of each hard region is at most 50% of the hardness of each superhard region.

FIELD

This disclosure relates to a superhard insert for a rotary earth borer tool.

BACKGROUND

Rotary earth borer tools are used for drilling holes into the earth in industries such as oil and gas exploration, well development and construction. Rotary drill bits for rock boring may comprise a plurality of superhard inserts mounted onto a drill bit body. In use, the head is rotated at high speed and with great force, rotationally driving the superhard inserts against the wall and end of a hole to remove rock material by a shear cutting action. Inserts suitable for such uses may be referred to as “shear cutter” inserts and may comprise a layer of polycrystalline superhard material bonded onto a cemented carbide substrate. An example of a polycrystalline superhard material is polycrystalline diamond (PCD).

PCD is a superhard material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. PCD is used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. For example, PCD inserts are widely used within drill bits for boring into the earth in the oil and gas drilling industry. In many of these applications the temperature of the PCD material becomes elevated as it engages a rock formation, workpiece or body.

European patent number 0 278 703 discloses abrasive bodies having a cemented carbide core and abrasive cutting corners, wherein the abrasive cutting corners may be of the same material or a different material. An abrasive body may comprise a layer of bonded ultra-hard abrasive particles bonded to a substrate, and ultra-hard abrasive particles may be diamond or cubic boron nitride.

PCT patent application publication number WO2002/022311 discloses a tool insert comprising a cemented tungsten carbide substrate having a plurality of pre-sintered recesses formed therein. An embodiment of the tool insert consists of a section of the substrate to which are bonded four abrasive bodies at each of the four corners of the section.

U.S. Pat. No. 5,607,024 discloses a superhard insert having a cutter end mounted on support member. The cutter end is a disk or tablet shaped form having polycrystalline diamond grains bonded within a binder comprised principally of cobalt. This tablet or disk is then securely attached to the cylindrical support member by means of a conventional high temperature and high pressure sintering process.

U.S. Pat. No. 7,533,740 discloses a cutting element having a substrate including an end surface and a periphery, where the end surface extends to the periphery, wherein a “TSP” material layer is formed over only a portion of the end surface and extends to the periphery. In one embodiment, the TSP is mechanically locked with the cutting element.

There is a need for a superhard insert for a rotary earth borer tool, the superhard insert having reduced cost or superior properties, particularly for boring into the earth or drilling or otherwise degrading rock formations.

SUMMARY

As used herein, “superhard” means a Vickers hardness of at least 25 GPa.

Viewed from a first aspect, there is provided a superhard insert for a rotary earth borer tool, comprising a cutter end having a peripheral cutter edge, at least part of the peripheral cutter edge being defined by a plurality of edges of a plurality of alternate hard and superhard regions, the edges of the superhard regions arranged spaced apart from each other and separated by edges of hard regions; the hardness of each hard region being at most 50% of the hardness of each superhard region.

The edges of the hard regions may wear more rapidly than those of the superhard regions in use to improve the cutting effect of the superhard regions.

In some embodiments, at least part of the peripheral cutter edge are angular, rounded, chamfered or bevelled.

As used herein, a rake surface is a surface of a cutting insert over which flows material removed by the cutting action of the superhard insert, such material typically being in the form of pieces called “chips”. A rake angle is the inclination of a rake face relative to the surface of the workpiece or other body being cut, bored into or degraded, a positive rake angle permitting chips to move away from the workpiece and a negative rake angle directing chips towards the workpiece.

In some embodiments, the cutter end includes a plurality of rake surfaces. The plurality of rake surfaces may be inclined at different angles with respect to each other, and may be arranged radially between the peripheral cutter edge and a region remote from the peripheral cutter edge, and may be a designated first face, second face, and so forth, starting from the peripheral cutter edge.

In some embodiments, the cutter end comprises two, three, four, five or even ten or more edges of superhard regions.

In some embodiments, the superhard inserts have a generally cylindrical or disc-like form. In some embodiments, the superhard inserts have substantially two-, three-, four- or even five-fold rotational symmetry about a central axis when viewed in a plan view of the cutter end.

The superhard insert may, in some embodiments, be re-usably mounted onto a tool, to assist in reducing the effective cost of the superhard insert by extending its working life.

In one embodiment, the cutter end comprises a hard central region remote from the peripheral cutter edge and is disposed centrally between the plurality of superhard regions. In one embodiment, the central hard region includes a raised or boss portion. The raised or boss portion may be formed integrally with the support body or secured to it by mechanical, braze or adhesive means.

In some embodiments, the raised or boss portion advantageously functions as a chip breaker in use, wherein chips formed of the material being bored or degraded are deflected away from the cutter end, thereby reducing wear of the cutting face.

In one embodiment, the cutter end comprises at least one cutter face that depends downward from the raised or bossed portion toward the peripheral cutter edge.

A negative rake angle may be achieved without needing to modify the angle at which the superhard insert is secured to the tool carrier.

In one embodiment, a superhard region lies on a rake face having a positive rake angle. In one embodiment, the central region includes a raised or boss portion from which part of the rake face depends downward, another part of the rake face adjacent the peripheral cutter edge extending upwards to form a positive rake angle, resulting in a scoop-like feature on the cutter end.

In one embodiment, each superhard region has a marking for identifying it.

Two or more superhard regions having different hardnesses or other property may be readily identifiable. The user may use the markings to select the superhard region most suitable for a desired application or workpiece material (e.g. type of rock formation). In one embodiment, the markings may be inscribed onto hard regions adjacent respective superhard regions.

In some embodiments, the superhard insert comprises a plurality of spoke structures projecting radially outward, each spoke comprising a superhard structure.

In some embodiments, each of at least one of the superhard region has generally converging or generally diverging sides when viewed in a plan view of the cutter end. Such embodiments may be configured so as to present a substantially constant or otherwise as desired superhard edge length as the region wears in use.

The length of the edge may remain substantially constant throughout the working life of a superhard insert, thus prolonging the performance of the cutter as it is progressively worn away in use.

In some embodiments, the Vickers hardness of each superhard region is at least about 40 GPa, at least about 50 GPa or at least about 60 GPa. In some embodiments, at least one of the superhard regions comprises material having a mean Young's modulus of at least 900 GPa, at least about 1,050 GPa or at least about 1,100 GPa.

In some embodiments, each hard region has a hardness at least 20% or at least 30% that of each superhard region. In one embodiment, each hard region comprises cemented tungsten carbide material.

In one embodiment, the superhard insert comprises a plurality of superhard structures comprising superhard material, the superhard structures bonded, clamped or otherwise joined to a support body. In some embodiments, the support body comprises material having a mean Young's modulus of at least about 60%, at least about 70%, or at least about 80% of that of each of the superhard regions.

In general, the smaller the difference between the mean Young's modulus of the support body and the superhard structures, the more robust may be the cutter insert, and the less likely may be the risk of the superhard structures becoming detached from the support body or fracturing.

In one embodiment, the support body comprises cemented tungsten carbide.

In one embodiment, the support body comprises superhard material, such as diamond or cubic boron nitride (cBN) in granular or particulate form.

The presence of superhard material in the support body may have the effect of increasing the stiffness of the superhard insert and may reduce the risk of fracture of the superhard structures.

In some embodiments, at least one of the superhard structures is secured to the support body by means of a pin, rivet, bolt or the like, or is clamped to the support body by a clamping means. In some embodiments, the support body comprises a through-hole configured to accommodate a securing pin, rivet, bolt or the like. In some embodiments, the securing pin, rivet, bolt or the like is threaded.

Some embodiments may be particularly suitable for being secured to a tool body by means of a pin or screw means because they have a central region that is not superhard and into which a through-hole may be formed to accommodate a pin, rivet or screw.

As used herein, “polycrystalline diamond” or PCD means a material comprising a mass of substantially inter-grown diamond grains, forming a skeletal structure defining interstices between the diamond grains, the material comprising at least 80 volume % of diamond.

In one embodiment, each superhard region comprises PCD material, preferably thermally stable PCD. In some embodiments, the PCD material has a diamond content of at least about 88 volume % or at least about 90 volume %. In some embodiments, the PCD material has a diamond content of at most about 99 volume %.

In some embodiments, at least one of the plurality of superhard regions comprises PCD material made by a method including subjecting the PCD or its precursor to a pressure greater than about 6 GPa, at least about 7.0 GPa or even at least about 8.0 GPa.

Some embodiments in which the superhard structure comprises PCD may comprise PCD sintered at high pressures which may be sufficient to result in enhanced diamond contiguity and enhanced inter-grain bonding, more homogeneous spatial distribution of the diamond grains, less porosity and lower overall solvent/catalyst content, and the PCD may have greater hardness, abrasion resistance and elastic or Young's modulus.

In some embodiments, at least one of the plurality of superhard regions comprises PCD material comprising diamond grains having mean diamond grain contiguity of at least about 60.5 percent or at least about 61.5 percent. In general, the higher the diamond grain contiguity, the less likely it may be for the superhard insert to fracture.

In some embodiments, at least one of the plurality of superhard regions comprises PCD material having an interstitial mean free path of at least about 0.05, at least about 0.1, at least about 0.2 or at least about 0.5 microns. In some embodiments, at least one of the plurality of superhard regions comprises PCD material having an interstitial mean free path of at most 1.5 microns, at most about 1.3 microns or even at most about 1 micron.

The combination of the high contiguity and/or high homogeneity and/or reduced content of metallic solvent/catalyst within the PCD on the one hand, and a size distribution comprising at least two peaks or modes, preferably at least three peaks or modes, on the other may result in substantial improvement in wear resistance and other properties of the PCD.

In one embodiment, least one of the plurality of superhard regions comprises PCD material comprising diamond grains having a multi-modal size distribution. In some embodiments, the PCD material comprises diamond grains having mean size of at most about 20 microns, at most about 10 microns, at most about 7 microns or even at most about 5 microns. In one embodiment, the PCD material comprises diamond grains having mean size of at least about 0.1 microns.

In one embodiment, the PCD comprises diamond grains having the size distribution characteristic that at least 50 percent of the grains have mean size greater than 5 microns, and at least 20 percent of the grains have mean size in the range from 10 to 15 microns.

The volume of superhard material incorporated therein may be reduced or minimised, which is important as superhard materials may be costly to manufacture and may be prone to high tensile residual stresses.

Viewed from a further aspect there is provided a rotary drill bit comprising a superhard insert as described above or herein.

Viewed from another aspect there is provided an earth boring tool comprising a superhard insert as described above or herein. In one embodiment, the earth boring tool may be a rotary drilling bit for boring into rock, for example for the purpose of extracting oil or gas.

DRAWINGS

Non-limiting embodiments will now be described with reference to the accompanying drawings of which:

FIG. 1A shows a schematic perspective view of an embodiment of a superhard insert.

FIG. 1B shows a schematic longitudinal cross section view along the line A-A in FIG. 1A.

FIG. 2 to FIG. 8 show A) schematic perspective views of embodiments of superhard inserts and B) schematic longitudinal cross section views along the line A-A in respective A).

FIG. 9 shows a perspective view of an embodiment of a superhard insert as well as a partly exploded perspective view of the embodiment of a superhard insert.

FIG. 10 show perspective view of a support body and clamp means for an embodiment of a superhard insert.

FIG. 11 shows a schematic perspective view of part of an embodiment of a rotary drill bit for earth boring, comprising a plurality of embodiments of a superhard insert.

The same references are used to refer to the same features in all drawings.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to FIG. 1A and FIG. 1B, an embodiment of a superhard insert 100 for a rotary earth borer tool (not shown) comprises a cutter end 110 having a peripheral cutter edge 120, at least part of the peripheral cutter edge 120 being defined by a plurality of edges 120 a, 120 b, 120 c, 120 d, 120 e and 120 f of a plurality of alternate hard regions 122 a, 122 b and 122 c and superhard regions 124 a, 124 b and 124 c, the edges of the superhard regions 124 a, 124 b and 124 c arranged spaced apart from each other and separated by edges of hard regions 122 a, 122 b and 122 c. The hardness of each hard region 122 a, 122 b and 122 c being at most 50% of the hardness of each superhard region 124 a, 124 b and 124 c. The superhard insert comprises a plurality of superhard structures 130 a, 130 b and 130 c mounted into a plurality of respective recesses formed into the periphery of a cemented carbide support body 140, each of the superhard structures having a respective surface exposed at the cutter end 110 to provide respective superhard regions 124 a, 124 b and 124 c of the cutter end. Each of the superhard structures has a respective edge forming an edge of a respective superhard region 124 a, 124 b and 124 c of the cutter end.

With reference to FIG. 2, an embodiment of a superhard insert, 100, appears generally elliptical when viewed from above the cutting end 110 and comprises a pair of PCD structures 130 a and 130 b that lie on the major elliptical axis A-A of the cutter end 110, each presenting respective superhard regions 124 a and 124 b on the cutter end 110.

With reference to FIG. 3 and FIG. 4, an embodiment of a superhard insert, 100, is generally triangular with three rounded corners when viewed from above the cutter end 110 and each of three PCD structures 130 a, 130 b and 130 c is located at a respective rounded corner.

With reference to FIGS. 5A and B, an embodiment of a superhard insert 100 comprises three spoke formations 150 a, 150 b and 150 c projecting radially from a central region 160 of the cutter end, each spoke bearing a respective PCD structure 130 a, 130 b and 130 c.

With reference to FIGS. 6A and B, an embodiment of a superhard insert 100 comprising a raised or boss portion 180 on the cutter end 110. The raised or boss portion, 180, may function as a chip breaker in use. The raised or bossed portion, 180, may be formed integrally with the support body, 140, or it may be secured to it by mechanical, braze or adhesive means (not shown)

With reference to FIGS. 7A and B, an embodiment of a superhard insert 100 comprising plurality of PCD structures 130 a, 130 b and 130 c, each having a respective exposed surface on a cutter end 110. A clamp member 182 is secured to the working surface 110 by means of a pin, rivet, bolt or the like 190, a lip 184 of the clamp member 182 extending over the exposed surfaces 124 a, 124 b and 124 c of each PCD structures 130 a, 130 b and 130 c. The lip 184 may help secure the PCD structures 130 a, 130 b and 130 c in place. In one embodiment the clamp member 182 provides rake faces at the cutter end 110.

With reference to FIGS. 8A and B, an embodiment of a superhard insert 100 comprises a plurality of PCD structures 130 a, 130 b and 130 c, each having a respective exposed cutting surface 124 a, 124 b and 124 c lying on a respective rake face 186 a, 186 b and 186 c that depends downward from the raised or bossed central portion 180 to the peripheral cutter edge 120. In some embodiments a through-hole is provided to permit the superhard insert 100 to be secured to a tool carrier (not shown) such as an earth boring bit by means of a pin, rivet, bolt or the like 190. In one embodiment with reference to FIG. 10, each of the rake faces 186 a, 186 b and 186 c is disposed at a different angle to each other and each of the rake faces 186 a, 186 b and 186 c has a respective visible marking which may be used to identify the angle or the grade of the respective PCD structure 130 a, 130 b and 130 c, or both.

With reference to FIG. 9, an embodiment of a superhard insert 100 comprises a support assembly 200 that further comprises a cutter support structure 210 and a base 220, the cutter support structure 210 being securable to the base by means of a mechanical locking mechanism. The locking mechanism may comprise at least one recess 220 a, 220 b and 220 c formed into the base 220 or into the cutter support structure 210 or both, and at least one cooperating tongue or projection 230 formed into the cutter support structure 210 or base 220.

With reference to FIG. 10, an embodiment of parts of a superhard insert comprises a support body 140 and a clamp means 142. PCD structures (not shown) may be clamped to the support body 140 by clamp means 142.

With reference to FIG. 11, an embodiment of a drill bit 300 for earth and rock boring, wherein a plurality of embodiments of superhard inserts 100 according to the invention are mounted to a carrier body 310. The superhard inserts 100 are mounted with one PCD structure at least partially protruding from the carrier.

The cutter inserts may be affixed to the support body by various means, including brazing, adhesive material, mechanical means (e.g. inter-locking with the support body) or it may be integrally bonded to the support body during the step in which the PCD is sintered, as is conventional. Preferably the PCD structures are sintered and processed prior to their being secured to the support body. This has the benefit that the PCD material can be prepared independently of the support body to which it is ultimately secured, thus removing certain constraints in making the material, such as selection of the type solvent/catalyst for diamond and whether the interstices of the PCD contain filler material.

The homogeneity or uniformity of a PCD structure may be quantified by conducting a statistical evaluation using a large number of micrographs of polished sections. The distribution of the filler phase, which is easily distinguishable from that of the diamond phase using electron microscopy, can then be measured in a method similar to that disclosed in EP 0974566 (see also WO2007/110770). This method allows a statistical evaluation of the mean thicknesses of the binder phase along several arbitrarily drawn lines through the microstructure. This binder thickness measurement is also referred to as the “mean free path” by those skilled in the art. For two materials of similar overall composition or binder content and mean diamond grain size, the material that has the smaller mean thickness will tend to be more homogenous, as this implies a finer scale distribution of the binder in the diamond phase. In addition, the smaller the standard deviation of this measurement, the more homogenous is the structure. A large standard deviation implies that the binder thickness varies widely over the microstructure, i.e. that the structure is not even, but contains widely dissimilar structure types.

Images used for the image analysis should be obtained by means of scanning electron micrographs (SEM) taken using a backscattered electron signal. Optical micrographs may not give sufficient contrast. Adequate contrast is important for the measurement of contiguity since inter-grain boundaries may be identified on the basis of grey scale contrast.

The contiguity may be determined from the SEM images by means of image analysis software. In particular, software having the trade name analySIS Pro from Soft Imaging System® GmbH (a trademark of Olympus Soft Imaging Solutions GmbH) may be used. This software has a “Separate Grains” filter, which according to the operating manual only provides satisfactory results if the structures to be separated are closed structures. Therefore, it is important to fill up any holes before applying this filter. The “Morph. Close” command, for example, may be used or help may be obtained from the “Fillhole” module. In addition to this filter, the “Separator” is another powerful filter available for grain separation. This separator can also be applied to color- and gray-value images, according to the operating manual.

In order to obtain a measure of the grain sizes, a method known as “equivalent circle diameter” is used, in which a circle equivalent in size for each individual microscopic area identified to be binder phase in the microstructure. The collected distribution of these circles is then evaluated statistically. In much the same way as for the mean free path technique, the larger the standard deviation of this measurement, the less homogenous is the structure.

Diamond grain contiguity, κ, is a measure of diamond-to-diamond contact and/or bonding and is calculated according to the following formula using data obtained from image analysis of a polished section of PCD:

κ=100*[2*(δ−β)]/[(2*(δ−β))+δ], where δ is the diamond perimeter, and β is the binder perimeter.

The diamond perimeter is the fraction of diamond grain surface that is in contact with other diamond grains. It is measured for a given volume as the total diamond-to-diamond contact area divided by the total diamond grain surface area. The binder perimeter is the fraction of diamond grain surface that is not in contact with other diamond grains. In practice, measurement of contiguity is carried out by means of image analysis of a polished section surface, and the combined lengths of lines passing through all points lying on all diamond-to-diamond interfaces within the analysed section are summed to determine the diamond perimeter, and analogously for the binder perimeter.

EXAMPLES

Embodiments of the invention are described in more detail with reference to the examples below, which are not intended to limit the invention.

Example 1

A PCD disc was prepared. Raw material diamond powder was prepared by blending diamond grains from sources having a different mean size in the range from about 1 micron to about 15 microns. The mean grain size of the blended mix was about 10 micrometres. The blended mix was formed into an aggregated mass and sintered onto a cobalt-cemented cemented tungsten carbide (WC—Co) substrate at a pressure of about 6.8 GPa and a temperature of about 1,500 degrees centigrade by means of an ultra-high pressure furnace, as is well known in the art.

After sintering the sintered composite compact article was removed from the apparatus. The compact comprised a layer of PCD integrally bonded onto the substrate. Microstructural data for the PCD is shown in table 1. The diamond content of the PCD layer was about 92 percent by volume, the balance being cobalt and minor precipitated phases, the cobalt having infiltrated from the substrate into the aggregated diamond mass during the sintering step. The diamond grains within the PCD structure had a multimodal size distribution. Image analysis was used to analyse the inter-growth of the diamond grains as well as the homogeneity of their spatial distribution within the PCD. The grain intergrowth and contact can be expressed in terms of diamond grain contiguity, and the mean contiguity of the PCD was 62.0 percent (±1.9 percent). The interstitial mean free path of the PCD was about 0.74 (±0.62) micrometres.

TABLE 1 Mean diamond Diamond Filler mean Diamond grain grain size^((a)), content of PCD, free path, contiguity, micrometres volume percent micrometres percent 11 (5.5)^((b)) 92 (1) 0.7 (0.6) 62 (2.0) ^((a))mean grain size measured as equivalent circle diameter (ECD) ^((b))the values in parentheses are the respective standard deviations

The cemented carbide substrate was then removed from the composite compact by grinding, leaving an un-backed, free-standing PCD disc. The PCD disc was ground to a thickness of about 2.2 micrometres, and then cut into three segments by means of electro-discharge machining (EDS), the shape of each segment being substantially as shown in FIG. 3. All three PCD segments were then treated (leached) in acid to remove substantially all of the cobalt solvent/catalyst material throughout the entire PCD structure, as is well known in the art.

A substrate substantially as shown in FIG. 3 support was machined from a cemented tungsten carbide body. When viewed from above, the substrate had a generally triangular shape, with rounded corners. A recess was machined into the substrate at each rounded corner, the size and shape of the recessed being matched to accommodate of the PCD segments, which were then brazed into the recesses. 

1. A superhard insert for a rotary earth borer tool, comprising a cutter end having a peripheral cutter edge, at least part of the peripheral cutter edge being defined by a plurality of edges of a plurality of alternate hard and superhard regions, the edges of the superhard regions arranged spaced apart from each other and separated by edges of hard regions; the hardness of each hard region being at most 50% of the hardness of each superhard region.
 2. A superhard insert as claimed in claim 1, wherein the cutter end comprises a hard central region remote from the peripheral cutter edge, the central hard region including a raised or boss portion operable to deflect chips formed of a material being bored or degraded away from the cutter end.
 3. A superhard insert according to claim 1, wherein at least one superhard region has an identification marking.
 4. A superhard insert according to claim 1, comprising a plurality of spoke formations projecting radially outward, each spoke comprising a superhard structure.
 5. A superhard insert according to claim 1, wherein one or more or each of the at least one of the superhard regions has generally converging or generally diverging sides when viewed in a plan view of the cutter end.
 6. A superhard insert according to claim 1, wherein the Vickers hardness of each superhard region is at least 40 GPa.
 7. A superhard insert according to claim 1, wherein one or more or each of the superhard regions comprises PCD material.
 8. A superhard insert according to claim 1, wherein the at least one of the plurality of superhard regions comprises PCD material comprising diamond grains having mean diamond grain contiguity of at least about 60.5 percent.
 9. A superhard insert according to claim 1, wherein the at least one of the plurality of superhard regions comprises PCD material having an interstitial mean free path of at least 0.05 microns and at most 1 micron.
 10. A rotary drill bit comprising a superhard insert as claimed in claim
 1. 11. An earth boring tool comprising rotary drill bit as claimed in claim
 10. 